1. Technical Field
The present invention relates to apparatus used for installing construction materials in general and to an automatic impact nailing and dimpling apparatus for driving a nail and setting a dimple to a predetermined depth in gypsum wallboard in particular.
2. Description of Prior Art
Gypsum board, also called wallboard and drywall, comprises processed gypsum which is sandwiched between sheets of paper. The board is usually provided in standard sheets 4 feet wide by 8 to 14 feet in length, 1/4 to 1" thickness.
In many applications, such as in the construction of residential wood framed homes, the board is attached to wooden studs by nailing the board to the studs. The nails used typically comprise a cupped head. As each nail is driven through the wallboard and into the stud, it is countersunk in the wallboard. In the process of countersinking the nail in the wallboard, a dimple is formed in the wallboard. The dimples thus formed and butt joints between adjacent boards are then taped and covered with a wallboard compound for providing a smooth uniform surface. Thereafter the surface is painted or covered with a plaster for providing an attractive and aesthetically pleasing appearance.
In the past, the nailing of wallboard to a wooden stud has been done using a conventional wallboard hammer, a single-stroke automatic impact hammer or the like.
In using a wallboard hammer, a nail is hammered into the wallboard and the stud until the base of the head of the nail is flush with the surface of the wallboard. Thereafter, a single stroke of the hammer using the convex surface of the hammer countersinks the nail and at the same time forms a dimple in the wallboard.
A principal disadvantage of the above-described method for installing wallboard is that the head of the nail is struck by the convex surface of the hammer before the convex surface of the hammer contacts the surface of the wallboard. This tends to cause the head of the nail to pierce the paper covering of the wallboard. Also, if the nail is not driven perpendicular to the wallboard, the sharp edge of the head of the nail will tend to pierce the paper covering the wallboard. Once the surface paper covering is pierced, it loses its integrity which reduces the holding ability of the cup headed nail.
Another disadvantage of the above-described method for installing wallboard is that it is time consuming.
Still another disadvantage of the above-described method is that it is difficult to set nails and dimples repeatedly at uniform and preferred depths.
In a typical prior known single-stroke automatic impact nailer and dimpler there is provided a piston member and nail set assembly which is pneumatically driven in a single-stroke fashion, a nail feeding mechanism which automatically feeds nails to a position beneath the nail set, a dimpler having a convex exterior surface with a hole centrally located therein which is activated by the piston member for creating a dimple in the wallboard as the nail is being set, and a triggering mechanism to control the operation of the apparatus.
In operation, the nail is driven through the hole in the dimpler by the piston and when the piston strikes the dimpler, it causes the dimpler to dimple the wallboard.
A principal disadvantage of the above-described single-stroke automatic-type nailing and dimpling apparatus is that, in general, there is no means provided in the apparatus for automatically controlling the depth to which a nail and a dimple is set in the wallboard. As a consequence, if the air pressure in the apparatus varies or the hardness of the wood studs to which the wallboard is nailed varies, the depth to which each of the nails is driven cannot be accurately controlled. This may result in nails not being driven deep enough or driven too deeply. If the nails are not driven deep enough, they will not be properly countersunk and if the dimpler is not driven deep enough, the paper will not be properly dimpled. Alternatively, if the nails and dimpler are driven too deep this can cause the nails and/or the dimpler to tear the surface paper, causing the nails to lose their holding ability.
Another disadvantage of prior known automatic nailing and dimpling apparatus is that in such apparatus there is generally no means, such as a sole plate or housing, for insuring that a nail is hammered into the wallboard perpendicular to the wallboard. This often results in a sharp edge of the nail pressing into the paper covering of the wallboard resulting in a greater tendency for the nail to cut through the paper covering of the wallboard as described above.